Tilting Gravity Casting Method for manufacturing Knuckle

ABSTRACT

A tilting gravity casting apparatus, a die includes a ladle that stores a molten metal and the molten metal is poured through a pouring gate into a cavity of the die when the die is tilted. The cavity accommodates a cylindrical protrusion for forming a closed-end hole in a bearing support portion of a knuckle, and the cavity has a pressing boss portion located along an axial line of the cylindrical protrusion. Before a die tilt step of tilting the die is completed, a press step of pressing the molten metal in the pressing boss portion by using a pressing pin and a pouring gate block step of blocking the pouring gate with a block member are initiated.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a casting method for manufacturing a knuckle, which is a part that connects a wheel supporting bearing to a suspension.

2. Background Art

A tilting gravity casting method in which a die includes a hopper (ladle) that stores a molten metal and the molten metal is poured into a cavity in the die through a pouring gate when the die is tilted is well known as described, for example, in Patent Literature 1 mentioned below.

Further, casting an automobile knuckle, which is a part that connects a wheel supporting bearing to a suspension, by using a tilting gravity casting method is well known as described in Patent Literature 2 mentioned below.

However, the tilting gravity casting method described in Patent Literature 1, in which a gas pressing step is carried out to press a molten metal in a cavity, may cause the following situations in some cases: The cavity in a die cannot be filled with the molten metal all the way down to the end of the cavity; and a cast product cannot be sufficiently free of shrinkage cavities and other casting defects.

Further, in the tilting gravity casting method described in Patent Literature 2, in which a molten metal feeder is provided in a position above a cavity of a die and gravity acting on the fed molten metal is used to cause the molten metal to reach the end of the cavity, since an automobile knuckle including arms extending in radial directions has a complicated shape, only the gravity acting on the fed molten metal does not allow the molten metal to reach the end of the cavity, resulting in insufficient prevention of shrinkage cavities and other casting defects in some cases.

PRIOR ART LITERATURES

Patent Literature 1: Japanese Patent No. 4,203,093

Patent Literature 2: Japanese Patent Laid-Open No. 2011-104613

The present invention therefore has been made in view of the problems with related art described above. An object of the present invention is to provide a tilting gravity casting method for manufacturing a knuckle that is excellent in filling a die cavity with a molten metal and is capable of forming a knuckle sufficiently free of casting defects.

SUMMARY OF THE INVENTION

The present invention has been made to achieve the object described above. A tilting gravity casting method for manufacturing a knuckle according to the present invention is a tilting gravity casting method for manufacturing a knuckle by using a tilting gravity casting apparatus 1, in which a die 2 includes a ladle 7, which stores a molten metal, and the molten metal M is poured through a pouring gate 5 into a cavity 6 of the die 2 when the die 2 is tilted. The cavity 6 accommodates a cylindrical protrusion 4B for forming a closed-end hole in a bearing support portion of the knuckle, and the cavity 6 has a pressing boss portion 6A located along an axial line of the cylindrical protrusion 4B. The method includes a die tilt step of tilting the die 2, a press step of pressing the molten metal M in the pressing boss portion 6A by using a pressing pin 23, and a pouring gate block step of blocking the pouring gate 5 with a block member 18, and the press step and the pouring gate block step are initiated before the die tilt step is completed.

It is preferable that after the press step is initiated, the pouring gate block step be initiated.

It is further preferable that the molten metal M is a semi-solidified slurry made of an aluminum alloy, and that a solid phase ratio of the semi-solidified slurry in the ladle 7 range from 5 to 10%.

According to the tilting gravity casting method for manufacturing a knuckle of the present invention, the cavity can be filled with the molten metal all the way down to the end of the cavity, and a knuckle can be sufficiently free of casting defects.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a tilting gravity casting apparatus for use in a tilting gravity casting method for manufacturing a knuckle according to an embodiment of the invention;

FIG. 2 is a perspective view of a block member;

FIG. 3 is a view describing a state in which a die is tilted from the state shown in FIG. 1 and a pressing pin starts pressing operation;

FIG. 4 is a view describing a state in which the die is further tilted from the state shown in FIG. 3 and a block member blocks a pouring gate;

FIG. 5 is a view describing a state in which the die tilt step is completed; and

FIG. 6 is a cross-sectional view of a knuckle before it is cut off.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

A tilting gravity casting method for manufacturing a knuckle according to an embodiment of the present invention will be described with reference to the drawings. A description will first be made of a tilting gravity casting apparatus 1 used to perform the tilting gravity casting method for manufacturing a knuckle according to the present embodiment. A tilting gravity casting apparatus 1 includes a die 2 formed of a lower fixed die 3 and an upper movable die 4, and the fixed die 3 and the movable die 4 define a pouring gate 5 and a cavity 6, as shown in FIG. 1. In the present embodiment, a groove formed in a movable die partition surface 4A and a fixed die partition surface 3A define the pouring gate 5. A ladle 7 is fixed to the fixed die 3 and stores a molten metal M, such as an aluminum alloy.

The fixed die 3 is fixed to an upper surface 8 a of a base 8. The lower end of each guide shaft 9 is fixed to the base 8, and the upper end of each of the guide shafts 9 is fixed to a top plate 10. A hydraulic cylinder 11 is fixed to an upper surface 10 a of the top plate 10, and the leading end of a cylinder rod 12, which passes through the top plate 10, is connected to a movable plate 13, which is disposed below the top plate 10. When the hydraulic cylinder 11 is driven, the movable plate 13 is guided along the guide shafts 9 and movable between the base 8 and the top plate 10 upward and downward in FIG. 1. Connection shafts 14 are provided below the movable plate 13 and connect the movable plate 13 to the movable die 4. The movable die 4 is therefore movable along with the movable plate 13 between the base 8 and the top plate 10 upward and downward in FIG. 1.

The tilting gravity casting apparatus 1 includes a tilting mechanism (not shown). The tilting mechanism is a well-known mechanism, such as that disclosed in Patent Literature 1 described above. The tilting mechanism includes a tilting shaft provided in the base 8 and extending in the direction perpendicular to the plane of view of FIG. 1, a support arm (not shown) that supports the tilting shaft, and a tilting motion drive device attached to the support arm. The tilting mechanism is capable of tilting the base 8 and the die 2 by about 90 degrees at a predetermined speed from the horizontal state shown in FIG. 1 in the direction indicated by the arrow α.

A hydraulic cylinder 15 is fixed to an upper surface 4 a of the movable die 4. A cylinder rod 16 of the hydraulic cylinder 15 is connected to a block member 18 via a coupling 17 in a hole 4 b formed in the movable die 4. The block member 18 has a circular-column-shaped head 18 a, which is accommodated in the coupling 17, and a square-column-shaped shaft 18 b, as shown in FIG. 2. When the hydraulic cylinder 15 is driven, the leading end of the shaft 18 b enters the pouring gate 5.

The pouring gate 5, through which the molten metal M moves, has a rectangular cross-sectional shape when taken along the direction perpendicular to the plane of view of FIG. 1, and is defined by: a groove formed in the movable die partition surface 4A; and the fixed die partition surface 3A, in such a way that the pouring gate 5 extends rightward and leftward in FIG. 1. The pouring gate 5 is blocked when the shaft 18 b of the block member 18 described above enters the pouring gate 5 and the leading end of the shaft 18B abuts or approaches the fixed die partition surface 3A.

A hydraulic cylinder 20 is fixed to a lower surface 8 b of the base 8 via support rods 19. A cylinder rod 21 of the hydraulic cylinder 20 is connected to a pressing pin 23 via a coupling 22. The pressing pin 23 passes through the base 8 and is disposed in a hole 3 a formed in the fixed die 3. When the hydraulic cylinder 20 is driven, the leading end of the pressing pin 23 enters the pressing boss portion 6A, which will be described later, and the pressing pin 23 presses the molten metal M in the cavity 6.

To form a closed-end hole C1 (see FIG. 6) at a bearing support portion of a cast knuckle, the movable die 4 has a cylindrical protrusion 4B, which protrudes downward in FIG. 1. The central axis of the cylindrical protrusion 4B substantially coincides with the central axis of the pressing pin 23 described above. The cylindrical protrusion 4B is disposed in the cavity 6 and forms the closed-end hole C1 in the bearing support portion. The cavity 6 has the pressing boss portion 6A defined by the fixed die 3 and located along the axial line of the cylindrical protrusion 4B and in a lower end portion of the cavity 6. As shown in FIG. 6, an excess metal C2 formed by the pressing boss portion 6A and other portions is cut off a cast product along the broken line after the casting is completed. The closed-end hole C1 in the bearing support portion is thus processed into a through hole.

An extruding pin (not shown) is provided in the die 2. After the movable die 4 is parted from the fixed die 3, the extruding pin can extrude the molten metal M having solidified in the pouring gate 5 and the cavity 6 out of the die 2. Further, an air gap around the extruding pin forms a gas discharge path (not shown) that passes through the die 2, and a degassing device (not shown) is connected to the gas discharge path. The degassing device can suck and discharge gases in the cavity 6 in a die tilt step that will be described later and can supply the gas discharge path with air in a parting agent application step that will be described later.

A description will next be made of a tilting gravity casting method for manufacturing a knuckle using the tilting gravity casting apparatus 1. In the tilting gravity casting method for manufacturing a knuckle, a molten metal preparation step of storing the molten metal M in the ladle 7 is first carried out to achieve the state shown in FIG. 1.

A die tilt step is then initiated, in which the die 2 is tilted from the state shown in FIG. 1 by about 90° in the direction indicated by the arrow α so that the molten metal M in the ladle 7 is poured through the pouring gate 5 into the cavity 6. The die 2 is tilted by the tilting mechanism (not shown) at a predetermined speed.

A press step and a pouring gate block step are initiated before the die tilt step is completed. When the die 2 is tilted, the molten metal M in the ladle 7 is poured through the pouring gate 5 into the cavity 6. At a timing when the molten metal M is still left in the ladle 7 and the pressing boss portion 6A is filled with the molten metal as shown in FIG. 3, the press step of driving the hydraulic cylinder 20 to cause the pressing pin 23 to enter the pressing boss portion 6A in the cavity 6 is initiated. Initiating the forward motion of the pressing pin 23 at this timing allows the molten metal in the cavity 6 to come into intimate contact with the die 2 so that the molten metal is shaped into a knuckle C, which is the cast product.

The pouring gate block step is then carried out, in which the hydraulic cylinder 15 is driven to cause the block member 18 to enter the pouring gate 5 and the leading end of the block member 18 is caused to abut (or approach) the fixed die partition surface 3A so that the pouring gate 5 is blocked (see FIG. 4). Initiating the press step and the pouring gate block step before the die tilt step is completed as described above to cause the pressing pin 23 to press the molten metal in the pressing boss portion 6A with the pouring gate 5 blocked with the block member 18 allows a surface layer in, for example, the end of the cavity (such as end of knuckle arm) that tends to separate from the die 2 due to solidification shrinkage to be pressed against the die 2. Further, the molten metal M corresponding to the loss due to the solidification shrinkage can be forced inside by pressure in the press step, whereby the knuckle C (see FIGS. 5 and 6), which is the cast product, can be sufficiently free of shrinkage cavities and other casting defects. The tilting operation continues after the press step is completed but is terminated when the state shown in FIG. 5, which is the state after the state shown in FIG. 1 is tilted by about 90°, is achieved, and the die tilt step is completed.

When a die cooling device (not shown) causes the molten metal in the cavity 6 to solidify, the hydraulic cylinder 20 is driven to retract the pressing pin 23 leftward in FIG. 5, and then a die open step is carried out. In the die open step, the hydraulic cylinder 11 is driven to move the movable plate 13 along with the movable die 4 rightward in FIG. 5 so that the movable die 4 is parted from the fixed die 3. The following steps are then sequentially carried out: a cast product removal step of removing a knuckle C as a cast product from the die 2 by using the extruding pin (not shown) provided in the die 2; a parting agent application step of applying a parting agent onto the pouring gate 5 and the cavity 6; and a die clamping step of driving the hydraulic cylinder 11 to move the movable plate 13 along with the movable die 4 leftward in FIG. 5 so that the movable die 4 abuts the fixed die 3. Finally, the tilt mechanism is used to restore the state of the die 2 shown in FIG. 1. The tilting gravity casting method for manufacturing a knuckle has been described above.

The tilting gravity casting method for manufacturing a knuckle according to the present invention are not limited to those described in the above embodiment, and a variety of changes and modifications can be made thereto to the extent that they fall within the scope of the claims. For example, in the embodiment described above, the pressing pin 23 is disposed on the side where the fixed die 3 is present, but the pressing pin 23 may instead be disposed on the side where the movable die 4 is present.

Further, in the embodiment described above, the press step is completed before the die tilt step is completed, but the initiated press step may be allowed to continue after the die tilt step is completed.

Further, in the embodiment described above, the press step is completed before the die tilt step is completed, but after the die tilt step is completed, the locked pressing pin may be unlocked and the press step may be resumed.

In the embodiment described above, the molten metal M, such as an aluminum alloy, is stored in the ladle 7. Instead, the molten metal M stored in the ladle 7 may be replaced with a semi-solidified slurry made of an aluminum alloy in a solid-liquid coexistence state. Setting a solid-phase ratio, which represents the solid-liquid ratio of the molten alloy in the ladle 7, to fall within an appropriate range (5 to 10%) and then carrying out the die tilt step allows the semi-solidified slurry in the ladle 7 to flow into the cavity 6 and fill the pressing boss portion 6A with the semi-solidified slurry. Thereafter, performing the tilting gravity casting method in such a way that the press step and the pouring gate block step are initiated before the die tilt step is completed as in the embodiment described above allows production of a cast knuckle having excellent quality with a small amount of segregation.

DESCRIPTION OF THE REFERENCE NUMBERS

-   1 Tilting gravity casting apparatus -   2 Die -   3 Fixed die -   3A Fixed die partition surface -   4 Movable die -   4A Movable die partition surface -   4B Cylindrical protrusion -   4 a Upper surface -   4 b Hole -   5 Pouring gate -   6 Cavity -   6A Pressing boss portion -   7 Ladle -   8 Base -   8 a Upper surface -   8 b Lower surface -   9 Guide shaft -   10 Top plate -   10 a Upper surface -   11 Hydraulic cylinder -   12 Cylinder rod -   13 Movable plate -   14 Connection shaft -   15 Hydraulic cylinder -   16 Cylinder rod -   17 Coupling -   18 Block member -   18 a Head -   18 b Shaft -   19 Support rod -   20 Hydraulic cylinder -   21 Cylinder rod -   22 Coupling -   23 Pressing pin -   M Molten metal -   C Knuckle (cast product) -   C1 Closed-end hole -   C2 Excess metal 

1. A tilting gravity casting method for manufacturing a knuckle by using a tilting gravity casting apparatus in which a die includes a ladle that stores a molten metal and the molten metal is poured through a pouring gate into a cavity of the die when the die is tilted, with the cavity accommodating a cylindrical protrusion for forming a closed-end hole in a bearing support portion of the knuckle, and with the cavity having a pressing boss portion located along an axial line of the cylindrical protrusion, the method comprising: a die tilt step of tilting the die; a press step of pressing the molten metal in the pressing boss portion by using a pressing pin; and a pouring gate block step of blocking the pouring gate with a block member, wherein the press step and the pouring gate block step are initiated before the die tilt step is completed.
 2. The tilting gravity casting method according to claim 1, wherein after the press step is initiated, the pouring gate block step is initiated.
 3. The tilting gravity casting method according to claim 1, wherein the molten metal is a semi-solidified slurry made of an aluminum alloy, and a solid phase ratio of the semi-solidified slurry in the ladle ranges from 5 to 10%.
 4. The tilting gravity casting method according to claim 2, wherein the molten metal is a semi-solidified slurry made of an aluminum alloy, and a solid phase ratio of the semi-solidified slurry in the ladle ranges from 5 to 10%.
 5. A tilting gravity casting apparatus for manufacturing a knuckle, in which a die includes a ladle that stores a molten metal and the molten metal is poured through a pouring gate into a cavity of the die when the die is tilted, the apparatus comprising: a block member that blocks the pouring gate; and a pressing pin that presses the molten metal, wherein the cavity accommodates a cylindrical protrusion for forming a closed-end hole in a bearing support portion of the knuckle, the cavity has a pressing boss portion located along an axial line of the cylindrical protrusion, and the pressing pin presses the molten metal in the pressing boss portion. 